Method of preventing casing and/or tubing damage in steam injection well

ABSTRACT

Oil is produced from an underground oil-yielding stratum by injecting through a well into said stratum a stream of hot injection fluid obtained by mixing steam and water at the surface of the earth prior to introduction into said well. The water reduces the temperature of the steam to a valve which is not detrimental to the well casing and/or tubing. In one embodiment, the well may be used in a &#39;&#39;&#39;&#39;huff and puff&#39;&#39;&#39;&#39; process and then as an injection well in a direct drive process.

United States Patent [72] Inventor Archie J. Cornelius 3388.744 6/1968 Fincher et al 166/303 Bartlosville. Okla. 3.434.544 3/1969 Satter et al 166/303 [2| Appl. No 787,669 3.456.734 7/1969 Dean et al 166/303X 12?] d 2 13 OTHER REFERENCES l atente une K 1.

. eplmger, C. H. Economrc Considerations Affecting [73] Asslgnee Humps Petroleum Company Steam Flood Prospects. In Producers Monthly, 29(5), May

1965. pp 14- 16, 1821. (Copy in 166- 303) Willhite, G. Paul, at al. Design Criteria For Completion of [54] METHOD OF pREvENTlNG CASING AND/0R Steam injection Wells ,ln J. Petroleum Technology, Jan.

TUBING DAMAGE 1N STEAM INJECTION WELL 1967 pp l 21 (Cop in 303) 12 Claims, 1 Drawing Fig. P y

rimary Examiner-Ian A. Calvert [52] US. Cl 166/263,

166/303 Attorney Young and Qurgg [51] lnt.Cl EZlb 43/24 [50) Field of Search 166/272, ABSTRACT; on is produced f an underground 1 303, 57, 2362 ing stratum by injecting through a well into said stratum a 56 R f d stream of hot injection fluid obtained by mixing steam and l 1 e erences e water at the surface of the earth prior to introduction into said UNlTED STATES PATENTS well. The water reduces the temperature of the steam to a 1,231,895 7/1917 Jacobus 236/ l 2 valve which is not detrimental to the well casing and/or tubing. 3,237,692 3/1966 Wallace et al. 166/303 In one embodiment, the well may be used in a huff and puff" 3,254,716 6/1966 Fitzgerald et a1. 166/303X process and then as an injection well in a direct drive process.

IO i 1 (W 4 7 I /V I 1 4 7 P 7 5 E d 16 I 7 A, g I" i 4 PATENT EU un nan 3,5 1 822 INVENTOR. A. J. CORNELIUS A TTORNEYS METHOD OF PREVENTING CASING AND/R TUBING DAMAGE IN STEAM INJECTION WELL This invention relates to the production of oil by thermal stimulationv Oil production by various thermal stimulation methods is known in the art. These methods, in general, comprise supplying heat to an underground oil-yielding formation or stratum to stimulate oil production by changing one or more conditions in the formation, e.g., decreasing the viscosity of the oil, or increasing the formation pressure. Thermal stimulation methods employed include various in situ combustion methods, various types of steam injection, and the injection of hot water. In all of these methods the general object has been to introduce the maximum amount of heat into the formation. Thus, in all of said methods the downhole equipment, e.g., the casing, tubing, etc., in the well or wells is exposed to temperatures greater than about 450 F. In many wells this results in a cracking, buckling, and/or a parting of the casing and/or the tubing, as well as damage to cement.

In one method of well stimulation utilizing hot water it has been proposed to introduce heated water through one pipe, introduce steam through another pipe, and mix said steam and water in the bottom of the well so that the water is at a maximum temperature just prior to its introduction into the oilbearing stratum. In many instances this method has only limited applicability in wells of any appreciable depth because of the excessive steam temperatures required.

The present invention provides a solution for the abovedescribed difficulties by eliminating exposure of the well tubing and/or casing, or other downhole equipment in the well, to detrimental high temperatures.

Broadly speaking, the present invention comprises providing a stream of hot injection fluid, for injection through a well into an underground formation, by mixing steam and water at the surface of the earth prior to introduction into said well.

An object of this invention is to provide an improved method of oil production. Another object of this invention is to provide a method for producing a hot injection fluid for injection into an oil-yielding stratum. Another object of this invention is to provide a method for thermally stimulating production of oil from an oil-yielding stratum by injecting a hot injection fluid into said stratum. A further object of this invention is to provide a method of hot water injection through a well into an oil-yielding stratum which prevents damage to downhole equipment in the well such as the casing, tubing, etc. Other aspects, objects, and advantages of the invention will be apparent to those skilled in the art in view of this disclosure.

Thus, according to the invention, there is provided, in a method for producing oil from an underground oil-yielding stratum penetrated by at least one well provided with a casing and/or a tubing string, the steps of: (a) generating steam; (b) mixing said steam, at the surface of the earth, with a stream of water to obtain a stream of hot injection fluid having a temperature less than the temperature which is detrimental to said tubing or casing under the conditions of use in said well; and (c) injecting said stream of hot injection fluid through said well into said stratum in an amount and for a period of time sufficient to improve the flow characteristics of said oil.

A number of advantages are realized in the practice of the invention. For example, by mixing steam and water at the surface of the earth none of the downhole equipment, e.g., tubing and/or casing, is subjected to detrimental high temperatures. The temperature of the final fluid can be readily controlled to any desired temperature independent of the well depth and/or the amount of the fluid to be actually injected. In contrast, when the steam and water are mixed in the well, at least the conduit or pipe carrying the steam is subjected to detrimental high temperatures.

Another advantage is more efl'icient use of steam generation equipment, resulting in savings in both investment and operating costs. As discussed hereinafter, there is a distinct advantage in employing the steam generator(s) to generate steam rather than employing said generator(s) as hot water heater(s). Furthermore, by generating a high-temperature steam and mixing same with water, only the water charged to the steam generator must be treated. Thus, the major portion of the water used in the process is not treated. This also effects significant savings in operating costs. The untreated water used in the process can be a raw water from any suitable source. Usually, said raw water will be cold," i.e., at ambient temperature, e.g., 40 to F. However, raw water having higher temperatures can also be used. Still another advantage of the invention is that said raw water can be formation water in those instances where the formation is sensitive to fresh water.

The steam used in the practice of the invention can be at any suitable temperature which is greater than the temperature desired on the hot injection fluid. In many instances, it will be desirable that said steam have a temperature of at least 500 F., or higher, for convenience or efficiency in operating the steam-generating equipment.

The invention is applicable to oil-yielding underground formations or strata such as oil sands, tar sands, etc. The invention is particularly applicable to formations or strata containing high viscosity oils which are difficulty flowable or even nonflowable under reservoir conditions. The invention is also applicable to formations containing oils of low to medium viscosity. The method of the invention can be utilized as a primary recovery method, or as a secondary recovery method,

e.g., where the sands have been previously produced by conventional primary methods.

In the practice of the invention the hot injection fluid will be injected into the formation being treated in an amount and for a period of time sufficient to significantly alter flow characteristics of oil contained in the formation, e.g., lower the viscosity of the oil at least about 10 percent or more, preferably at least 50 percent or more. Generally speaking, and as a guide to those skilled in the art, the amount of hot injection fluid injected into a formation will be within the range of from about 25,000 to 50,000 pounds per hour, depending upon interrelated factors such as formation thickness, formation permeability, and the amount of formation face exposed in the well. Typical injection rates will usually be within the range of about 250 to 750 lbs. per foot of open interval in the well per hour. However, it is within the scope of the invention to inject amounts of hot injection fluid which are outside said range.

It is desirable that the hot injection fluid utilized in the practice of the invention have a temperature which is not greater than about 425 F. so as to prevent damage to the casing and/or tubing under the conditions of use in said well. This is desirable in order that the most economical grades of low carbon steel can be employed in the casing and/or tubing. It is preferred that said hot injection fluid have a temperature in the range of about 350 to about 400 F. In most instances, said hot injection fluid will be maintained under sufficient pressure to maintain same in essentially liquid phase, i.e., as liquid water. However, it is within the scope of the invention to employ a two-phase mixture of steam and water.

The invention is applicable to formations or strata located at appreciable depths below the surface of the earth, e.g., at least about 500 feet, and is particularly applicable to formations located at least about 1,000 feet below the surface of the earth. The following Table I illustrates this feature of the invention.

Referring to said table 1, it will be noted that for a formation located at a depth of l,000 feet, and having a formation pressure of at least 433 p.s.i.g., it will be impossible to mix water and steam in such a well without subjecting either the tubing and/or the casing to a temperature in excess of 425 F. A column of water filling a tubing or casing in such a well will have a head of at least 433 p.s.i. Thus, in order to inject steam into this head of water it is required that the steam pressure be at least equal to the head of water. Under these circumstances the steam will have a temperature of about 450 F. Actually, one would probably use a steam pressure somewhat above the minimum requirements. This would increase the steam temperature still more. Furthermore, in many instances the formation pressure or permeability will require that even higher steam pressures be used. However, by mixing the steam and water at the surface of the earth in accordance with the invention one can avoid subjecting the tubing and/or casing to the high steam temperatures.

The drawing illustrates diagrammatically several embodiments of the invention. Referring to said drawing, a stratum is penetrated by a well [2 which is provided with a casing 14 and a tubing string 16. If desired, although it is not necessary in the practice of the invention, a packer may be positioned around tubing 16 so as to seal off the annulus between said tubing 16 and casing 14. Said casing 14 is provided with perforations 18 in the portion thereof which extends into stratum 10.

A boiler or steam generator 20 is provided aboveground and a steam line 22, having control valve 24 disposed therein, is connected with a mixing tee 26. A water conduit 28, having control valve disposed therein, is also connected into said mixing tee 26. Conduit 32, having valve 34 disposed therein, is also connected to said mixing tee and to the upper end of tubing string 16. Outlet conduit 36, having valve 37 disposed therein, is connected into said conduit 32. Outlet conduit 38, having valve 39 disposed therein, is connected to the casing l4.

In the practice of one embodiment of the invention a hog injection fluid is prepared by passing water via conduit 28 into mixing tee 26 and introducing sufficient steam via conduit 22 into said mixing tee 26 to increase the temperature of said water to a value not greater than about 425 F. If desired, suitable automatic controls can be installed on valves 24 and 30 to control the amounts of said steam and water in accordance with the temperature desired on the injection fluid. Said hot injection fluid is passed via conduit 32 into tubing 16 and introduced into formation 10 through perforations 18 in casing 14. The hot injection fluid is introduced in an amount and for a period of time sufficient to cause same to invade formation 10 for an appreciable distance, e.g., about 10 to 50 feet or more, initially. When a sufficient amount of the hot injection fluid has been injected into the formation, the well is closed in by closing the valves at the wellhead so as to initiate a soaking period. Said soaking period is not essential in the practice of the invention but is usually preferred. Thus, said soaking period can range from zero up to 30 days, or longer, during which heat is absorbed into the formation. After a suitable soaking period, depending upon the characteristics of the formation and the oil contained therein, the well can be placed on production by opening either valve 37 or valve 39, as desired, and depending upon whether or not a packer has been installed around tubing 16. This will reduce the pressure in the well and permit oil together with hot injection fluid to flow therefrom. If desired, a pump can be installed on the downhole end of tubing 16 to pump oil and water from the well. Effluent from the well is passed via either conduit 36 or 38 to suitable oil separation and recovery means.

The above-described steps of injecting, soaking, and then producing the formation can be repeated cyclically in any manner that proves desirable from an economic standpoint depending upon the characteristics of the formation and the oil contained therein. The length of the injection period, the length of the soaking period, and the length of the production period will all depend upon the characteristics of the formation and the oil contained therein. Said periods can extend over days or months. After a number of cycles, one or more, the amount of oil left in the formation will be diminished, and at the same time the temperature of the formation will have been increased, to such an extent that the effective radius of injection surrounding well 12 will have extended out into the formation for a substantial distance. At this time, if desired, a second well 40, substantially like said well 12, can be completed into said stratum 10. If desired, said second well can have been previously completed and shut in during said cycles. Then, if desired, the production process can be changed from the previous method which can be considered a huff and puff" process to what is essentially a direct drive process. Preferably, this change is made after a number of said cycles which is sufficient to heat substantially all of said stratum between said wells. in this embodiment of the invention the hot injection fluid introduced into the formation via well 12 will pass through the formation 10, driving oil ahead of same, and then through perforations 42 in the casing of well 40. The fluids so driven into well 40 may be produced therefrom by opening one of the valves at the wellhead, or by means of a suitable pump on the downhole end of the tubing string.

The following illustrative embodiment will serve to further illustrate the invention. A well is completed into a producing formation located at a depth of 3,000 feet and having a reservoir pressure of approximately l,l00 p.s.i. and a reservoir temperature of approximately 134 F. The well is equipped with apparatus to facilitate both the introduction of fluids thereinto and the removal of effluent therefrom, similarly as illustrated in the drawing. Steam at a temperature of about 600 F. is mixed into water at ambient temperature (approximately 70 F.) in an amount sufficient to provide a hot injection fluid having a temperature of about 380 F. Injection of said hot fluid is started and continued for a period of 14 days, with the injection pressure averaging about 2,000 p.s.i. At the end of the l4-day injection period, injection of said hot fluid is terminated and the formation allowed to soak for 7 days. The pressure on the well is then reduced to start production. An initial production rate of about 500 barrels per day of oil is obtained during the first week. By the end of the first production cycle, 6 months later, this well is producing about I75 barrels per day of oil, significantly more than its former production rate of I40 barrels per day prior to the treatment with the hot injection fluid. At the end of said first production cycle the injection of the hot injection fluid is resumed. The cycle ofinjection and production is repeated until the reservoir being treated is depleted to a point where further production is no longer economically feasible, or until the formation has been heated to an extent making it attractive to steam-drive the oil from said well to another spaced-apart well.

The abovedescribed injection and production cycle is carried out employing steam-generating equipment designed for maximum thermal output of 20 million B.t.u. per hour in the form of percent quality steam. When this equipment is used directly as hot water-heating equipment to heat water to 380 F., liquid throughout restrictions limit the maximum thermal output to about 8 million B.t.u. per hour. This, when operating in accordance with the invention, e.g., employing said generating equipment to produce steam and using said steam to heat water, and mixing said steam and water at the surface of the earth, there is obtained an operating improvement of about 250 percent over employing said generators to produce hot water directly. Furthermore, by mixing the steam and water at the surface of the earth it is possible to control the temperature of the injected hot water independently of well depth and amount of water injected. This temperature control makes it possible to maintain the temperature of the injected hot water below temperatures at which damage to the well casing and/or tubing occurs.

While the invention has been described as being employed with one input-output well (well 12) and/or one output well (well 40), the invention is not so limited. The invention is apclosure.

lclaim:

1. In a method for producing oil from an underground oilyielding stratum penetrated by at least one well provided with a casing and/or a tubing string, the steps of:

a. generating steam having a temperature which is detrimental to said casing and/or tubing string;

b. mixing said steam, at the surface of the earth, with a stream of waterhaving a temperature less than said detrimental temperature, to obtain a stream of hot injection fluid having a temperature less than said detrimental temperature; and

. injecting said stream of hot injection fluid through said well and into said stratum in an amount and for a period of time sufficient to improve the flow characteristics of said oil.

2. A method according to claim 1 wherein said hot injection fluid of step (b).'has a temperature not greater than about 425 3. A method according to claim 2 wherein said hot injection fluid of step (b) has a temperature within the range of about 350 to about 400 F.

4. The method of claim 1 including the further steps of:

d. terminating the injection of step (c);

e. reducing the pressure on said well and allowing said oil having improved flow characteristics to flow into said well; and

f. recovering said oil from said well.

5. The method of claim 4 wherein: said stratum is penetrated by a second well spaced apart from said other well;

said steps (a), (b), (c), (d), (e), and (f) are repeated for a number of cycles sufficient to heat substantially all of said stratum between said wells; said second well is shut in during said cycles; then, after the last of said cycles, repeating said steps (a), (b), and (c); continuing the injection of said lastmentioned step (c) for a period of time sufficient to drive said oil into said second well, and said oil is produced from said second well.

6. The method of claim 5 wherein said hot injection fluid of step (b) has a temperature not greater than about 425 F.

7. The method of claim 6 wherein said hot injection fluid of step (b) has a temperature within the range of about 350 to about 400 F.

8. The method of claim 5 wherein: said steam is generated in a steam generation zone; said water is at substantially ambient temperature; said steam and said water are mixed downstream from said steam generation zone; and said hot injection fluid has a temperature within the range of about 350 to about 400 F.

9. The method of claim 1 wherein said stratum is penetrated by a second well spaced apart from said other well, said injection of step (c) is continued for a period of time sufficient to drive said oil into said second well, and said oil is produced from said second well.

10. The method of claim 9 wherein said hot injection fluid of step (b) has a temperature not greater than about 425 F.

11. The method of claim 10 wherein said hot injection fluid of step (b) has a temperature within the range of about 350 to about 400 F.

12. The method of claim 1 wherein: said steam is generated in a steam generation zone; said water is at substantially ambient temperature; said steam and said water are mixed downstream from said steam generation zone; and said hot injection fluid has a temperature within the range of about 350 to about 400 F. 

2. A method according to claim 1 wherein said hot injection fluid of step (b) has a temperature not greater than about 425* F.
 3. A method according to claim 2 wherein said hot injection fluid of step (b) has a temperature within the range of about 350* to about 400* F.
 4. The method of claim 1 including The further steps of: d. terminating the injection of step (c); e. reducing the pressure on said well and allowing said oil having improved flow characteristics to flow into said well; and f. recovering said oil from said well.
 5. The method of claim 4 wherein: said stratum is penetrated by a second well spaced apart from said other well; said steps (a), (b), (c), (d), (e), and (f) are repeated for a number of cycles sufficient to heat substantially all of said stratum between said wells; said second well is shut in during said cycles; then, after the last of said cycles, repeating said steps (a), (b), and (c); continuing the injection of said last-mentioned step (c) for a period of time sufficient to drive said oil into said second well, and said oil is produced from said second well.
 6. The method of claim 5 wherein said hot injection fluid of step (b) has a temperature not greater than about 425* F.
 7. The method of claim 6 wherein said hot injection fluid of step (b) has a temperature within the range of about 350* to about 400* F.
 8. The method of claim 5 wherein: said steam is generated in a steam generation zone; said water is at substantially ambient temperature; said steam and said water are mixed downstream from said steam generation zone; and said hot injection fluid has a temperature within the range of about 350* to about 400* F.
 9. The method of claim 1 wherein said stratum is penetrated by a second well spaced apart from said other well, said injection of step (c) is continued for a period of time sufficient to drive said oil into said second well, and said oil is produced from said second well.
 10. The method of claim 9 wherein said hot injection fluid of step (b) has a temperature not greater than about 425* F.
 11. The method of claim 10 wherein said hot injection fluid of step (b) has a temperature within the range of about 350* to about 400* F.
 12. The method of claim 1 wherein: said steam is generated in a steam generation zone; said water is at substantially ambient temperature; said steam and said water are mixed downstream from said steam generation zone; and said hot injection fluid has a temperature within the range of about 350* to about 400* F. 